Storage-Retrieval Interleaving in Automatic Warehousing Systems

Abstract

This paper extends work previously reported on storage assignment rules for automatic warehousing systems to include interleaving; that is, the sequencing of storage and retrieve requests. Using both continuous analytical models and discrete evaluation procedures, this paper compares the operating performance of several storage assignment/interleaving policies. The results indicate that significant reductions in crane travel time (and distance) are obtainable in some real-world and/or previously modeled situations via the proposed storage assignment/interleaving policies. These reductions may be directly translated into increased throughput capacity for existing systems. The storage assignment/interleaving policies may also be used to improve the design of proposed systems to achieve a more desirable balance between throughput and storage capacity. Although the system examined is a high-rise automatic warehouse, the results presented have implications for the warehousing function in general.

A survey of literature on automated storage and retrieval systems

“…Hausman et al (1976) prove that a L-shaped configuration with square-in-time boundaries for classes A, B and C is optimal when single command scheduling is applied in square-in-time racks. Graves et al (1977) demonstrate through simulation that this L-shaped configuration is close to optimal for dual command scheduling in square-in-time racks. Guenov and Raeside (1992) also study dual command scheduling and compare three different zone shapes.…”

“…Five often used storage assignment policies for AS/RSs are described here in more detail (see e.g., Hausman et al, 1976or Graves et al,1977. These rules are:…”

“…Travel time estimates (see Section 9) for both single and dual command scheduling in different types of AS/RS configurations are an appropriate analytical tool for comparing control rules (e.g., Hausman et al, 1976;Graves et al, 1977). With simulation more extensive experiments under stochastic conditions can be performed (e.g., Schwarz et al, 1978;Kaylan and Medeiros, 1988;Kulturel et al, 1999;Van den Berg and Gademann, 2000).…”

“…The possibility of performing dual command cycles depends on the availability of storage and retrieval requests. If both types of requests are available, dual command cycles give advantages with respect to travel times (Graves et al, 1977).…”

Robust Storage Assignment in Unit-Load Warehouses

“…Another example of a shared storage policy is the class-based turnover policy proposed by Hausman et al (1976), Graves et al (1977), and Schwarz et al (1978). Under this policy, storage locations are grouped into several classes.…”